large flows of sand into the AIWW. The fill template for the original inlet covers some 24 acres
and extends 518 m (1,700 ft) northward from the pre-project inlet south channel bank. The
Project's final excavation plan would require removal of 110,925 m3 (145,000 yd3) of sand from
Mason Creek, 256,275 m3 (335,000 yd3) from the sand trap and 260,100 m3 (340,000 yd3) from
the new inlet channel. Excavation to construct the initial project would result in a net quantity
of an estimated 612,000 m3 (800,000 yd3), with 206,550 m3 (270,000 yd3) placed to fill the
original inlet channel and 382,500 m3 (500,000 yd3) for beach nourishment .
An inlet maintenance frequency of 3 years was projected including dredging the sand trap
and an area contiguous with the north-channel bank of the inlet to situate the channel at the
northern limit of the "inlet corridor." Maintenance dredged material would be placed either
along the beaches of Figure Eight Island or further south along the north end of Wrightsville
Beach based on the results of the beach and inlet survey monitoring plan. In the event that
threshold sand losses exceed pre-established rates sand placement would occur along the affected
area(s) of inlet impact. Mason Creek hydraulic efficiency and alignment with the new inlet
channel are key elements in preventing high rates of inlet migration in future years. However, if
the maintenance to prevent this migration proves too costly, the initial project would provide an
estimated 10 years of protection prior to impacting development at the north end of Wrightsville
Beach. The resulting benefit-to-cost ratio, under this outcome would exceed 3:1 and provide
significant benefits and return on their investment under the worst-case situation.
Inlet Opening
Between January 2002 and April 15, 2002, the construction phase of the Mason Inlet
Relocation Project was completed. Two cutter-head hydraulic dredges (14 and 16 inches) and
several large capacity excavators worked concurrently to construct the project within the tight
time frame allowable by the project's permits. Mason Creek channel, excavated to a design
width of 140 ft and depth of 10 ft (NGVD) along a 1,400-m (4,580 ft) length, was dredged
between the new inlet and the AIWW at the same time that a second dredge excavated the
sedimentation basin, hydraulically moving sand 3 miles north onto the beaches of Figure Eight
Island. Simultaneously, a truck haul operation moved sand from the new inlet channel
excavation site on Figure Eight Island north to the beach nourishment site, placing sand onto the
landward portion of the berm template, with hydraulic placement of material onto the seaward
portion of the berm template. During the design and construction process a number of specific
challenges were encountered to which engineering solutions were found. In particular, the sheet
pile wall with geotextile containers to reinforce the tie-ins, proved to be a essential element of
the construction design when a strong nor'easter hit the site one week prior to the planned
opening of the new inlet nearly causing a near breach at the structure's terminus.
The new Mason Inlet channel was opened on March 7, 2002 during a neap tide phase with
the temporary sheet pile removed just prior to the beginning of an ebb tidal cycle. The following
day, the Mason Creek channel, plugged by a 60 m (200 ft) unexcavated section, left in place to
prevent extreme currents during the initial inlet opening, was dredged. Initial tidal flows
between Mason Creek and the AIWW exceeded 1.6 m/sec (5 ft/sec) and boats were advised to
remain away from the area until the inlet channel stabilized. Within a week of the new inlet's
opening, the outer ocean channel scoured to a depth of 1.5 m (5 ft), providing boaters an
opportunity to use the inlet. An aerial photograph of the site taken one week after the inlet's
opening (Fig. 5) shows the old and the new inlet channels. The original inlet channel was
subsequently closed on March 14, 2002 when a bridge of sand was pushed from the sand
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